Method of protecting subterranean metallic structures



Patented Dec. 13, 1949 UNIT ED STATES v. PA-T-El`1'l`f OFFICEMETHODmOFgPROSIECTING SUBTERR'ANEAN- i METALLIC STRUCTURES' Y Dick E.VStearns; Shreveport, La.v

Application Octoberxl, 1944,- Serial hlm-558,924

5 Claims.' (Cl. 204-147) This invention .relatesto `method and. means,of protecting subterranean or. buried metallic. structures fromelectrolysis and corrosiondue. to local action.

It is common.practicettoprevent such electrolysis andvcorrosion-.oisubsurface structures such as pipe lines or thelike vby.applyingto .the structure adirectcur-rent `volt'age'oi suchpolarity asto'causev the currenttolowin a direction to make deposit on the pipelinerather than to take material` from thepipe lineY or, other. structure.Such structuresV are usually:Ak coated. .with an insulating material butsuchinsulationeither has or develops weakA spots .at which, .acceleratedcorrosion or electrolysistakes place `andthe electrical protection justyreferred to tends .tcstopor atleast eife'ctivelyinhibit.thedeterioration otthe pipe line or other ,structureat suchdefective spotsin the insulation.

In applying. sucha voltage to a subterranean structure, theA presentcustom is, to.. install an anode yat a substantialdistance.away fromvthe pipe line .so .thatdirect .current .induced tolow from.. the anodeYto ythepipe line willbe spread over asubstantial length of. thepipeline. Because of the relative nearness of the conventionalanode-tothe pipeline-as compared to the extent of the pipe line overwhich protection from corrosion is desired,v there isV substantialwastage of electrical energy between the two extremities (of 0 the pipelinesectionunder Iprotection) receiving i the critical amount ofpotential required for protection. Efforts haveabeen-pmade'with a degreeof success towards increasing over-all efficiency byV using severalsmaller units'over a given extent of pipe line rather thanr'having onlyone lunit therefor. At best, howeverythefprotection units with thepresent system-must ine-placed every-few miles along apipe-line lorsimilar structurein order to give the'necessary prOtection and even thenthe protection afforded is not uniform and is unreliable.

lAs 'an example 'of `one ofthe vproblems encountered'with the Apresentlyused system, there is a result known as interferenceiwhich occurs wheretwo structures, one. of whichisprotected by the usual method,...approachA onerosa-each other. Someoffthe current from..v the buriedanode williowto anadacent. portion o the other structure, thence alongthat structure to the point ci nearest approach of the two structures,and then across to the structure being protected. This does not hurt thestructure being protected, but will quickly eat away or cori-ode theother structure and destroy it.

The present. invention. has for .its principal and general objecttheprovision of fully adequate and reliable protection for a pipeline orsimilar struct ture buried in the earth or .otherwise made subject tocorrosiondue to electrolysisand local electro? chemical action..

More specically itis an object of the present invention to provide moreyadequate .protection for such a structure with a smaller number oiunits than now necessaryandto make it. possible to place such units atthe most convenient points on the structure., Another objectVoftheloresent invention isV to provide a means for moreadequatelycontrolling the current flow by which the protection is'secured, as` compared with. inadequate current control of the methodsheretofore used..

Another object is to avoid the interference above described...

Other objects and advantages of this invention 'willbecome apparent fromthe followingdescription taken in connection with" the accompanyingdrawing wherein is set forth b'y way of illustration and example Voneembodiment of this invention.

In the drawing;

Fig. 1 is a view partly in. elevation Yand partly in longitudinal crosssection through a pipe line, illustratingY the apparatus employed andthe method of carrying jout'the present invention.

Fig. 2is atransverse crosssection'taken along the line '2"-2'of Fig; l.Y

Fig. 3 isa diagrammatic illustration showing the. applicationof theprotective voltage to a pipe or similar object 'to be protected in.accordance with this invention.

Referring more in detail to the drawing, the numeral l illustrates. apipeline which in this particular instance is' the structure to be.protected.' This pipeline .isprovidedwith an insulating coating 2'which' may generallyv speaking be of the type presently.4 employed onsuchlstruc'- tures such asy enamels or coatings having a coaltar baseoranyother suitablecoating material.

V,Such acoating k2 manif. desired,.be wrapped'inV a manner .suchlas nowemployed with a suitable brous insulating wrapper such. as indicated at3. It. willbe .understood that `upto this point. the 'practice describedis thesame. as that.. employed in connection vwith `the. presentprotection of buried pipe lines'.

In accordance with the present invention, there is added to the coatingson the structure to be protected, a sheathing or wrapping of sheet metalor metal foil 4. This sheet metal or metal foil may be of any suitablematerial but is preferably of some very light and thin material such asaluminum foil and is preferably of such a nature as to cover the entireor substantially the entire surface of the exterior of the insulatedstructure. With a pipe line or other structure coated or wrapped as justdescribed, it is put in place in the ground or in such other position aswould subject it to electrolysis and local action, and the negative poleof a direct current Voltage is applied to the structure to be protectedthe same as in the present system of protecting such structures.However, instead of connecting the other pole to an electrode buried ata substantial distance from the structure to be protected, the otherpole is connected directly to the sheathing 4 which covers substantiallythe entire surface of the insulation over the structure to be protected.

Inasmuch as the sheathing 4 is made of metal, and preferably of a metalwhich has a very low electrical resistance, it will assume substantiallythe same potential throughout its extent, because unless there are holesin the insulating coating underneath this sheathing, there will besubstantially no flow of current. Even if there is a considerable iiowof current, the extent of the metal sheathing provides a substantialpath for the flow of current and hence would tend to minimize anyvoltage drop due to such ow.

Inasmuch as the protective voltage is applied substantially uniformlyover the entire surface of the structure to be protected, and at aposition closely adjacent such structure, the protection afforded Willbe uniform and the voltage for providing such protection may besubstantially lower than that which has heretofore been employed.Furthermore, due to the excellent path provided for current flow and thefact that the anode extends along, substantially parallel to and inclose proximity to the structure to be protected,

only a relatively few points of application of the voltage will benecessary and these may be located more nearly where they may beconveniently tended. Also since the sheath which forms the anode isclose to the structure protected at all points and is between thatstructure and any adjacent structure, there will be no possibility ofinterference such as above described.

Although the method and means for protecting subterranean structures hasbeen described as applied to buried pipe lines or the like, it will beappreciated that it may also be applied to other structures such asburied tanks, cables and in fact any structure which is in such alocation that it is subjected to corrosion due to electrolysis and localaction.

It will also be appreciated that by the apparatus and method justdescribed there has been provided a means for carrying out andaccomplishing all of the objects and advantages sought by thisinvention.

Having described my invention, I claim:

1. The method of protecting buried metallic structures from corrosiondue to electrolysis and local action, which comprises coating the samethe positive and negative poles of a source of di- 4 rect currentelectric voltage to said sheath and metallic structure respectively.

2. The method of protecting buried metallic structures from corrosiondue to electrolysis and local action, which comprises coating the samewith an electrical insulator, sheathing the insulated coating of suchstructure with an electrically conductive sheath of sheet metal of foilthickness in close relation thereto, and applying the positive andnegative poles of a source of direct current electric voltage to saidsheath and metallic structure respectively.

3. The method of protecting buried metallic structures from corrosiondue to electrolysis and local action, which comprises coating the samewith an electrical insulator, wrapping the coated structure with a thinmetallic sheathing of foil thickness applied spirally over substantiallythe entire exterior surface of the structure in close relation thereto,and applying the positive and negative poles of a source of directcurrent electric voltage to said wrapping and said metallic structurerespectively. v

4. The method of protecting a pipe line of electrically conductingmaterial to be buried in the ground from corrosion due to electrolysisand local action comprising the steps of coating the pipe lineexteriorally with insulating material, applying a thin sheet of metalsurrounding the insulating material in close relation thereto andapplying the positive and negative poles of a source of direct currentelectric voltage to the sheet and pipe line, respectively.

5. The method of protecting a pipe line of electrlcally conductingmaterial to be buried in the ground from corrosion due to electrolysisand local action comprising the steps of coating the pipe lineexteriorally with insulating plastic material, then wrapping the coatedpipe line spirally with a fibrous wrapper, then wrapping the thus coatedpipe line with a metal wrapper of foil thickness in close relation withthe fibrous wrapper and then applying the positive and negative poles ofa source of direct current electric voltage to the metallic wrapping andpipe line, respectively.

DICK E. STEARNS.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 843,357 Partee et al. Feb. 5,1907 1,096,177 Marino May 12, 1914 1,867,984 Pistor July 19, 19321,871,125 McGary et al Aug. 9, 1932 FOREIGN PATENTS Number Country Date249,714 vItaly Aug. 7, 1926 408,799 Germany Jan. 30, 1925 OTHERREFERENCES Transactions of the Electrochemical Society, vol. 64 (1933),pages 115 to 123.

Technologic Papers of the Bureau of Stand ards, No. 52, Dec. 27, 1915,pages 33 to A37.

